Real time self differential global positioning system and method for a moving station in a local area, and terminal global positioning system using the same

ABSTRACT

A real-time self Differential Global Positioning System (DGPS) is developed for positioning a moving station in a local area. This DGPS system enables not only to minimize the error ranges without any additional expansive transmitting-receiving equipment, but also to calculate an accurate correcting value through a DGPS receiver. A method of the real-time self DGPS system comprises the steps of: (1) receiving a GPS signal of moving station contained data of satellite time and pre-measured moving station position, (2) calculating a correcting value from the moving station, (3) positioning the accurate moving station according to the correcting value and the GPS signal of moving station.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a Global Positioning System (GPS) and method for a moving station in a local area. More particularly, this GPS system relates to a technology of a real time self Differential Global Positioning System (DGPS) and method for positioning a moving station in a range of several kilometers and applying the technology to a terminal operation.

[0003] 2. Description of the Prior Art

[0004] In a couple of recent decades, so many cutting edge technologies are competitively developed to lead the world markets. One of technologies is the Global Positioning System (GPS) and Method that enable to determine a three-dimensional poison and time anywhere on or near the surface of the Earth for a moving station. The GPS system being operated at least four satellites enables to position a moving station by receiving data of satellite-based navigating location, speed and time through receivers. However, the conventional system has a wide error range of approximately 100 meters, which is not acceptable in reality. The large range of errors is due to the GPS (none-military GPS) orbit, delay of passing the Ionosphere and Troposphere and Selective Availability (SA).

[0005] As shown in FIG. 1, a typical configuration of conventional DGPS system illustrates a navigation system enabling to position a client through the process: a reference station being known the position, (1) calculates an error range in a pseudo distance according to the received data from a satellite, (2) transmits the calculated error range to the near by user, and (3) determines the real position. Next, (4) the DGPS system broadcasts the correcting message via a broadcasting system. The correcting message for correcting a position error is calculated according to the corresponded instant of GPS signal comparing the pre-measured position at the reference station with the calculated position according to the received GPS signals. For broadcasting the correcting message, the correcting message is transformed to a standard format of Radio Technical Commission for Maritime Services (RTCM). The transformed correcting message is modulated to the ultrahigh frequency by a modulator (5), transmitted through a transmitter (6), and received through a receiver (7) for reflecting on the calculation of the positions.

[0006] The errors contained in the GPS signals (i.e., errors caused from the GPS satellite orbit, GPS satellite time, delay of Ionosphere and Troposphere when the GPS signals pass through the layers of Ionosphere and Troposphere, interference of multi-channel and receiver noise) are considered as a common errors between the reference station and user excepting the interference of multi-channel error and receiver noise error. In order to delete or minimize these sorts of errors, the process is adopted the theory of decay.

[0007] Moreover, the published Korean Patent Application No. 1999-15845 and the registered Korean Patent No. 260253, are disclosed that: an effect of the DGPS is weakened or vanished as the distance between the DGPS reference station and user is farther (normally more than 100 Km), because the common errors has the characteristics of decay. To reduce or limit the occurrence of common errors, a plurality of reference stations must be established. A technique of minimizing error range is developed by properly modifying an error correction being calculated from more than 2 reference stations within a certain distance.

[0008] As shown in FIG. 2, a flow chart of the conventional DGPS performance is presented for positioning a client by adapting a plurality of reference stations. In step S0, a user's pseudo distance contained error is determined according to the GPS signals. In step S1, the correction values of pseudo distance (PRCi) are received from each DGPS reference station. In step S2, among the received correction values of pseudo distances between the reference stations and users, select only the correction values of pseudo distance being received within 100 Kilometers, and discard rest of the correction values. In step S3, calculate a space functional correlation ratio (Pwiu) between a reference station and user and a space functional correlation ratio (Pwiwj) between the reference stations. The step S4 determines a modifying value (Wi) for applying to error correction from the i-th reference station. The step S5 calculates the user's correction value (PRCm) of pseudo distance according to the modifying value (Wi) determined in the previous step 4 and the correction value of pseudo distance (PRCi) received from each reference station. The step S6 accurately calculates a final correction value (PRC) of pseudo distance by adding or subtracting the correction value of each reference station to the user's correction value of the pseudo distance calculated from each DGPS receiver. The step 7 determines an accurate final user's position according to the final correction value (PRC) and the user's pseudo distance (contained error) determined from the GPS signal (S0).

[0009] In order to apply the DGPS system, it requires installing the expensive DGPS receivers and additional transmitting equipments. Therefore, this system is not suitable to operate a plurality of moving stations due to the requirement of installing the expensive equipments. Another system of Post Processing DGPS is suggested to reduce the errors and operating cost. However, this system has difficulty to apply the real time DGPS.

SUMMARY OF THE INVENTION

[0010] In order to overcome the problems of the conventional GPS and DGPS as discussed above, a unique real-time self-Differential Global Positioning System (DGPS) of the present invention is developed for positioning the moving stations in the real time through a wireless modem within a range of several Kilometers (desirably in the range of 1˜2 Kilometers) in the local area. This new system enables not only to calculate, transmit and receive the correcting values via only the GPS receiver, but also to reduce error ranges to several decade centimeters or several centimeters, which is the same level as the DGPS without additional equipments.

[0011] The real-time self DGPS system for a moving station is operated under a circumstance that a client is communicated to a server through a wireless LAN network in a local area. The real-time self DGPS system comprises: a private reference station (10) being pre-detected its position by an accurate measurement includes a reference station GPS receiver (11) for positioning via satellites.

[0012] A moving station (30) includes a moving station GPS receiver (31) for detecting position via satellites and a first wireless modem (32) for transmitting RGPS signals. The RGPS signals contain the position data and satellite time data. The moving station GPS receiver (31) is connected to the first wireless modem (32) to transmit the signals.

[0013] A central control unit (40) comprises a TGPS receiver (41), a central control server (42) and a second wireless modem (43). The second wireless modem (43) is connected to the first wireless modem (32) of moving station (30) for communicating each other in a relatively short distance.

[0014] The TGPS receiver (41) is interfaced with the reference station GPS receiver (11) to receive the RGPS signals from the reference station. The TGPS receiver (41) performs to calculate a correction data (X′0, Y′0) from the received data and transmit the calculated correction data to a central control server (42).

[0015] The central control server (42) is interfaced with the second wireless modem (43) being received the RGPS signals from the moving station. The central control server (42) performs calculating the real position of moving station by correcting error from the received position RGPS signals of moving station. The position data is transformed to the coordinating values in the local area. The local area is defined within several kilometers.

[0016] A Terminal Global Positioning System (TGPS) being adopted a real-time self DGPS in a local area comprises: the position data being received through the existing wireless modem used for controlling and manipulating a job control data of the moving station without any additional transmitting-receiving equipments. The code of position data and job control data is comprised of a string including a distinguished head.

[0017] A method of real-time self DGPS comprises the processing steps of: at a specific moment, the central control server (42) receives a moving station GPS signal (Mgps_0) contained the data of satellite time (To) and moving station position (Xm0, Ym0) measured by a moving station GPS receiver (MGPS) (31) (S10). The received data of satellite time (To) of moving station GPS signal is transmitted to a TGPS receiver (41) (S12). Receiving the reference station GPS signal (Rgps_—2, Rgps_—1, Rgps_0, Rgps_1, Rgps_2) contained satellite time (To) data and position data (Xr, Yr) being measured by a reference station GPS (RGPS) receiver (11) of private reference station (10) close to the satellite time (To) in TGPS server (41). Selecting a position data (Xr0, Yr0) of reference station GPS signal corresponded to the satellite time (To) (S14). Calculating a correcting value (X′0, Y′0) according to the selected reference station GPS signal (Rgps_0) and stored actual position data (Xs, Ys) of reference station (S20). Calculating an error corrected actual position data (Xcm0, Ycm0) of the moving station according to the correcting value and the position data of moving station (S24).

[0018] Generally, the error ranges of the conventional GPS and DGPS systems are proportion to the distance between the reference stations. To increase the accuracy of DGPS system, the error must be reduced to an acceptable range of several decades of centimeters or several centimeters. To do so, the additional equipments are costly required for modifying the conventional GPS or DGPS system.

[0019] On the other hand, the DGPS system of the present invention establishes a private reference station within a several Kilometers in the relatively narrow local area. Through the existing wireless modems used for controlling and governing, the new DGPS system enables to transmit-receive a correcting value of GPS signals for accurately positioning the moving stations and reducing the error ranges without installing any expensive equipments.

[0020] Most GPS signal data measured by the conventional technique contains the wide and irregular error ranges if a moment when a moving station needs a correcting value is different a moment when a server transmits the correcting value. Thus, the conventional technique is not reliable because the error ranges are so wide and irregular every time.

[0021] Even though, the moment of requesting and receiving the correcting value of GPS signal data are different, the new technique of the new DGPS system enables to accurately calculate the correcting values and chase the trajectories of the moving stations by using a Log and satellite time data transmitted when the moving station requests the correcting value via the TGPS server.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a system configuration drawing illustrating a conventional Differential Global Positioning Systems (DGPS).

[0023]FIG. 2 is a flow chart of conventional Differential Global Positioning Systems (DGPS) applied to a plurality of the reference stations.

[0024]FIG. 3 is a system configuration drawing illustrating a real time self differential global positioning system (DGPS) of the present invention.

[0025]FIG. 4 is a flow chart of the real time self differential global positioning system (DGPS) of the present invention.

[0026]FIG. 5 is a data flowing drawing of the real time self differential global positioning system (DGPS) of the present invention.

[0027]FIG. 6 is a terminal global positioning system being adopted a real time self differential global positioning system (DGPS) of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] A unique real-time self Differential Global Positioning System (DGPS) for a moving station of the present invention is developed in order to overcome the problems of conventional GPS and DGPS systems as discussed above. The new DGPS system has capability of calculating, transmitting and receiving the correction values by using only the GPS receiver without additional equipments. The new DGPS system also enables to accurately position the moving stations in the real time through a wireless modem within a range of several Kilometers in a local area. Thus, the error range is reduced to the several decade centimeters or several centimeters.

[0029] The detailed description is presented accompanying with FIG. 3 through FIG. 6.

[0030] As shown in FIG. 3, a real-time self DGPS system for a moving station and TGPS adapting the real-time self DGPS system is composed of the GPS satellites (20˜23), private reference station (10), moving station (30) and central control unit (40).

[0031] The private reference station (10) being established at an accurately pre-measured position has a function of receiving data from the satellites (20˜23), calculating an error range in a pseudo distance and transmitting the calculated error range to the TGPS server. The conventional DGPS reference station is usually equipped a huge transmitting and receiving facilities to cover the several hundreds Kilometers of broadcasting. As comparing with the conventional DGPS, the private reference station (10) consists only a reference station GPS receiver (11) for detecting position via satellites. The TGPS system is also equipped a GPS receiver (11), which is same as the reference station GPS receiver (11), for accurately detecting position via satellites. Generally, more than one private reference stations are established in a radius of 2 Kilometers.

[0032] A moving station (30) includes a moving station GPS receiver (31) for detecting position via satellites (20˜23) and a first wireless modem (32) being used for transmitting GPS signals which are contained the position data and satellite time data. The transmitting speed of the wireless modems affects the accuracy of the real time positioning.

[0033] A central control unit (40) includes a TGPS receiver (41), central control server (42) and second wireless modem (43). The second wireless modem (43) communicates with the first wireless modem (32) in a relatively short distance. The TGPS receiver (41) (or PC) is interfaced with the reference station GPS receiver (11) for sequentially receiving the GPS signals, calculating correction data (X′0, Y′0) from the received signals and transmitting the calculated correction data to a central control server (42). The GPS signal data is stored in the central control unit (40), private reference station (10) or any other storing unit in the system on the basis of the satellite time. However, the data must be transmitted or received through the exclusive line for prompt communication.

[0034] The central control server (42) transmits only the satellite time data among the GPS signals received from the moving station (30) to the TGPS receiver (41). Then, the TGPS server (41) compares the received GPS satellite time with the stored GPS signal of reference station for selecting a corresponded GPS signal of reference station. The position data of the selected GPG signals is transformed to a coordinating value. The transformed coordinating value is compared with the precisely coordinated values of pre-measured reference station. The difference of transformed coordinating value and pre-measured coordinating value is a correction value.

[0035] On the other hand, the TGPS server (41) transmits the correcting values to the central control server (42). At the central control server (42), the position data of stored GPG signals of reference station is transformed to a coordinating value. The final corrected position of moving station is calculated from the difference of coordinating values between stored position data and transmitted correcting values.

[0036] The central control server (42) is interfaced with the second wireless modem (43) to receive the GPS signals from the moving station, and calculate real time position of the moving station by using correcting values from the received position data of GPS moving station.

[0037] A terminal Global Positioning System (TGPS) is adopted the real-time self-Differential Global Positioning System (DGPS). In the TGPS system, the central control server (42) has a function of job control server, too. This means that, the TGPS is operated under the client circumstance with the wireless LAN network and server in a terminal operating site without the extra server. The position data received via existing wireless modem to control and governing the job control data of moving station without any additional transmitting-receiving equipment. The position data and job control data comprise a string and distinguished header.

[0038] As shown in FIGS. 4 and 5, a method of real-time self DGPS in a local area comprises the processing steps of: in step S10, the central control server (42) receives a GPS signal (Mgps_0) of moving station containing data of satellite time (T0) and moving station position (Xm0, Ym0) being measured by a moving station GPS receiver (MGPS) (31) at a specific position and time.

[0039] In step S12, the data of satellite time (To) among the moving station GPS signal is transmitted to the TGPS receiver (41).

[0040] In step S13, the TGPS server (41) pre-stores the reference station GPS signal (Rgps_−2, Rgps_−1, Rgps_0, Rgps_1, Rgps_2) being contained satellite time (T) data and position data (Xr, Yr) measured by a reference station GPS (RGPS) receiver (11) of private reference station (10) at near the satellite time (To). The position data of GPS signal from the reference station contains a real position data (Xs, Ys) being accurately pre-measured from the reference station when the reference station is established.

[0041] In step S14, the TGPS server (41) receives the data of satellite time (T0) and the reference station GPS signals (T−2, Xr−2, Yr−2; T−1, Xr−1, Yr−1; T0, Xr0, Yr0; T1, Xr1, Yr1; T2, Xr2, Yr2; Xs, Ys) contained satellite time (T) data and position data (Xr, Yr), and select a reference station GPS signal (Rgps_0) being correspond to the satellite time (T0).

[0042] In step S16, the TGPS server (41) transforms the position data of reference station to a local coordinate value from the selected coordinate value (Xr0, Yr0).

[0043] In step S18, the GPS coordinates value (Xr0, Yr0) of the satellite time (To) subtracts from the basic coordinates value (Xs, Ys) of the position data of reference station by selecting the pre-measured position data of reference station.

[0044] In step S20, a correcting value (X′0, Y′0) of the real time at the satellite time (To) is calculated based on the selected reference station GPS signal (Rgps_0) and stored actual position data (Xs, Ys) of reference station.

[0045] In step S21, the central control server (42) transforms the position coordinating value (Xm0, Ym0) of moving station received from the wireless modem (32) of moving station to a local coordinating value.

[0046] In step S22, the position coordinating value (Xm0, Ym0) of the selected GPS signal of moving station is subtracted from the received correcting value (X′0, Y′0) of the real time at the satellite time (To).

[0047] In step S24, an actual position (Xcm0, Ycm0) of the moving station is calculated based on the correcting value and the position data of the moving station.

[0048] In step S26, finally, an actual position (Xcm0, Ycm0) of moving station is transformed to an accurate local position coordinating value.

[0049] A local coordinating system is a practical coordination being transformed from the GPS signal. Because the GPS coordinating system is used a global coordination, it is not suitable to position a moving station in a relatively narrowed local area.

[0050] The TGPS system of the present invention is designed for applying to a relatively narrowed local area within a range of 2 Kilometers. If a position data is transformed to a local coordinating system being controlled by a control server, it is convenient to directly use the position coordination data to the terminal operating site. The transformed data for the local area is displayed on a mapping screen of the operating site at a corresponded position.

[0051] For example, the practical locations or positions (Number of Block, Bay and Row; Yard Defined Information) of T/C or S/C are important in the terminal operation than the GPS positioning represented the several hundred meters or a couple of tens centimeters to the east or north from the reference station.

[0052] As shown in FIG. 6, an application of the GPS system applied to a terminal is illustrated for positioning containers and container transporting equipments of T/C or S/C in the terminal site. For example, it is necessary to control the prime mover or yard equipments such as a traveling crane (T/C) (50) or straddle carrier (S/C) (60) required for loading or unloading at the harbor through a monitor (44) operated by the supersonic label sensor (34). To control the equipments, a job control signal being issued by the control server (42) of central control unit (40) is transmitted through the wireless modems (43, 32) to the job processor (33) of the mobile equipment set (30′) and performed by a spreader controller (35).

[0053] At the terminal site, the TGPS is operated for controlling and watching the job performance under the client circumstance with a wireless LAN network and server without the additional receiving-transmitting equipments. Each of units has each wireless communicating system (modems) for transmitting and receiving the position data and job control data. This TGPS system does not require the expansive ultra-high frequency transmitting-receiving equipment used in the conventional DPGS system. Because this TGPS system is applied to the relatively narrow area within a several Kilometers, it is aimed to positioning the moving station via the control server rather than the client positioning via the GPS navigating system.

[0054] The TGPS system mainly aims to position the moving stations through the control server. The control server is able to position the moving stations for the following cases:

[0055] (1) A necessary data including the GPS position data is transmitted to the server when a moving station is requested a specific job.

[0056] (2) When a server is needed to position a specific moving station, the current GPS position data of the specific moving station is requested to transmit through a special message, and the current GPS position is identified by a response of the specific moving station.

[0057] (3) If a moving station is needed to identify its' current position, the moving station enables to identify its' present position by transmitting its' GPS position data to the server through a special message.

[0058] A code of job controlling used for transmitting data comprises a string message with a header and a separator (-)

[0059] For example: (1) AAA-GPS-2-3- . . .

[0060] (2) ABB-JOBS-JobA- . . .

[0061] wherein “AAA” or “ABB” represents a header, and “-” represents a separator.

[0062] In the examples, the string of position data are interpreted that AAA” or “ABB” represents a header, after a first separator “-” represents a GPS number, sequentially after the second separator “-” represents a local coordinating value. In the example (2), the string of position data is interpreted that, a job control data “JOBS” follows after the first separator “-”.

[0063] While the present invention has been described in detail with its preferred embodiments, it will be understood that it further modifications are possible. The present application is therefore intended to cover any variations, uses or adaptations of the invention following the general principles thereof, and includes such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains within the limits of the appended claims. 

What is claimed is:
 1. A real time self Differential Global Positioning System (DGPS) for a moving station being operated under a client circumstance with a wireless LAN network and server in a local area, said DGPS system comprises: a private reference station (10) being pre-measured its' position through accurate measurement, said private reference station (10) including a reference station GPS receiver (11) for detecting position via satellites (20˜23), a moving station (30) including a moving station GPS receiver (31) for detecting position via satellites, and a first wireless modem (32) for transmitting RGPS signals contained a position data and satellite time data from said moving station GPS receiver (31), a central control unit (40) including a TGPS receiver (41), a central control server (42) and a second wireless modem (43), said second wireless modem (43) communicating with said first wireless modem (32) in a short distance, said TGPS receiver (41) being interfaced with said reference station GPS receiver (11), received said RGPS signals from said reference station, calculated correction data (X′0, Y′0) from the received data, and transmitted said calculated correction data to said central control server (42), and said central control server (42) being interfaced with said second wireless modem (43), received said RGPS signals from said moving station, and calculated real position of said moving station by correcting error from the received RGPS signals of position data of moving station.
 2. A real-time self DGPS as claimed of claim 1, said local area is defined within a range of several kilometers, and said position data enabling to transform a position coordinating value in the local area.
 3. A terminal Global Positioning System (TGPS) being adopted a real-time self DGPS system in a local area, the TGPS system comprises: a private reference station (10) being pre-measured its' position through accurate measurement, said private reference station (10) including a reference station GPS receiver (11) for detecting position via satellites (20˜23), a moving station (30) including a moving station GPS receiver (31) for detecting position via satellites, and a first wireless modem (32) for transmitting RGPS signals contained a position data and satellite time data from said moving station GPS receiver (31), a central control unit (40) including a TGPS receiver (41), a central control server (42) and a second wireless modem (43), said second wireless modem (43) communicating with said first wireless modem (32) in a short distance, said TGPS receiver (41) being interfaced with said reference station GPS receiver (11), received said RGPS signals from said reference station, calculated correction data (X′0, Y′0) from the received data, and transmitted said calculated correction data to said central control server (42), and said central control server (42) being interfaced with said second wireless modem (43), received said RGPS signals from said moving station, and calculated real position of said moving station by correcting error from the received RGPS signals of position data of moving station, and a job control data and position data able to codify a code comprising a string with a header and a separator (-).
 4. A method of real time self Differential Global Positioning System (DGPS) in a local area comprises the processing steps of: receiving a moving station GPS signal (Mgps_0) at a central control server (42), said moving station GPS signal (Mgps_0) being contained data of satellite time (T0) and moving station position (Xm0, Ym0) which are measured via a moving station GPS receiver (MGPS) (31) at a specific position and time, transmitting said data of satellite time (T0) of moving station GPS signal to a TGPS receiver (41), receiving reference station GPS signals (Rgps_−2, Rgps_−1, Rgps_0, Rgps_1, Rgps_2) at the TGPS server (41), said reference station GPS signals being contained satellite time (T0) data and position data (Xr, Yr) which are measured via a reference station GPS (RGPS) receiver (11) of private reference station (10) at near to said satellite time (T0), selecting a position data (Xr0, Yr0) of reference station GPS signal being corresponded to said satellite time (T0), calculating a correcting value (X′0, Y′0) according to said selected reference station GPS signal (Rgps_0) and stored actual position data (Xs, Ys) of reference station, and calculating an error corrected real position (Xcm0, Ycm0) of said moving station according to said correcting value and position data of moving station. 